The advantages of the diesel or compression ignition engine for heavy duty industrial and certain automotive applications is well recognized. The application of compression ignition engines to aircraft applications has been considered as impractical throughout the years, particularly, because of the normal high weight to horsepower output ratio of such engines. It is believed that no significant number of compression ignition engines are in aircraft operation today. Likewise, there is a failure to recognize that compression ignition engines for aircraft operation offer a number of important advantages over the conventional spark plug ignited gasoline engine for such applications. These advantages include:
1. Significantly reduced risk of fire due to the absence of electrical ignition and the employment of a high flash point fuel. 2. Greater reliability due to the elimination of the principal sources of conventional aircraft engine failure, i.e. the magneto and spark plugs and associated wiring and contacts.
3. Greater fuel economy and, therefore, increased flight range.
4. Elimination in normally aspirated aircraft engines of carburetor icing and unwanted power variations with altitude, temperature and humidity.
5. More uniform fuel distribution between cylinders due to metered fuel injection.
6. Lower exhaust temperature resulting in greater efficiency and, in military operations, lower infra red signature of the engine exhaust.
7. Elimination of radio interference due to the diesel's non-electric ignition.
None of these advantages of diesel engines for aircraft applications, heretofore could be achieved, however, without paying the unacceptable weight penalty.
I have explored the early attempts to achieve improved aircraft engines, whether of spark or compression ignition and have recognized that early attempts may have employed good design but suffered from the limitations of available materials. An example is the use of sleeve valves. Creative work was done by Sir Harry Ricardo and recounted in his series of books "The High Speed Internal Combustion Engine," particularly Vol. 4, Copyright 1954 and his work and the work of others on sleeve valve engines was described in Chapter 6, entitled "The Sleeve Valve" of the volume "High Speed Valve Mechanisms" by Malvey, copyrighted in the 1960's.
I am aware that turbocharger designs for reciprocating aircraft engines often add greatly to the bulk, cost and complexity of the engine. Likewise, I have noted that the exhaust manifolding and system also adds to the bulk or volume of the engine installation and often adds both back pressure to the engine, reducing its thermal efficiency, and drag to the aircraft profile.
The cylinder design of most aircraft engines usually requires multiple studs with precise torquing and safety wiring of nuts to assure proper installation and operation. Unnecessary weight seems to be involved.